JPS5916195B2 - Method of producing oxygen by air separation - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION This invention relates to the separation of oxygen from air by means of a sheath, and more particularly, to a non-adiabatic system with an inverting heat exchanger for removing water vapor and carbon dioxide from a charge air. An improved method for separating oxygen from air using an air fractionation system.

In prior art production of oxygen and nitrogen from air, carbon dioxide and water vapor were removed from the charge air by external means such as molecular sieves, as exemplified by US Pat. No. 3,594,983.

However, molecular sieves used for this purpose are bulky and relatively expensive.

U.S. Patent 350 for Producing Nitrogen by Air Separation
In No. 8412, compressed air is cooled in a regenerative cooler in countercurrent heat exchange relationship with oxygen-enriched steam and nitrogen.

The most economical way to remove carbon dioxide and water vapor from charge air is to remove CO2 as a solid on the surface of a regenerative heat exchanger.
2 and water vapor, and by reversing the flow path between the incoming charge air and the low-pressure nitrogen exhaust stream, these contaminants leave the heat exchanger surface and sublimate into the vapor phase. I am forced to do it.

However, such regenerative heat exchangers have generally been used at high charge air pressures, for example on the order of about 10 atmospheres.

It is an object of the present invention to provide a method and apparatus for separating oxygen from air by sheathing while minimizing power consumption by reducing the pressure of the charge air, preferably to about 3 atmospheres or less. It is a purpose.

Another objective is to use an inverting heat exchanger to perform water vapor and carbon dioxide removal from the feed air at pressures of 3 atmospheres or less.

Another objective is to perform the separation of oxygen from the air using an inverting heat exchanger in conjunction with an air fractionator for the removal of carbon dioxide and water vapor while maintaining an air charge pressure not exceeding approximately 3 atmospheres. .

Another object is to enable the production of both liquid and gaseous oxygen products while maintaining air purification using the above method and apparatus utilizing an inverting heat exchanger.

CO from the feed air using a reversing regenerator in a process of the type disclosed in U.S. Pat. No. 3,508,412 using differential distillation to separate the air.

The capacity of the nitrogen-rich waste stream to carry away water vapor contaminants is 2.
(2) the pressure difference between the incoming air and the nitrogen-rich exhaust stream; and (2) the temperature difference between these two streams.

2 above at the cold end of the heat exchanger as the charge air pressure decreases, resulting in lower energy consumption.
The temperature difference between the two streams becomes more critical in allowing removal of CO2 and water vapor.

As the pressure of the charge air is reduced, the temperature difference between the charge air and the exhaust stream at the cold end of the reversing regenerator must be very carefully regulated.

This is especially true in the zone of the fractionation system so that the temperature difference between the charge air and the return nitrogen exhaust and oxygen product streams is extremely small, i.e. 1.7°C (3R) at 3 atmospheres. It requires that the heat and mass transfer relationships be determined very carefully.

According to the invention, the production of oxygen from air involves compressing the air to, for example, about 3 atmospheres and passing the compressed charge air through alternate passages of a reversing heat exchanger in heat exchange relationship with the nitrogen exhaust stream, thereby reducing the This is done by freezing the water vapor and CO2 on the surface of the heat exchanger passages.

By reversing the flow so that the low pressure nitrogen exhaust stream flows through the charge air passage, this causes sublimation and evaporation of CO2 and water vapor.

In a preferred operation, a portion of the charge air is withdrawn at an intermediate point in the inverting heat exchanger, and molecules flJ! It is further cooled at the bottom of the rack.

The main air flow passing through the heat exchanger is mixed with the cooled charge air exiting the fractionator, and the resulting mixture is charged through the first fractionation zone of the non-adiabatic fractionator to perform a differential black section, thereby converting it into oxygen. The rich liquid is condensed,
A first fractionation zone as described above operating at a charge air pressure of, for example, about 3 atmospheres is withdrawn and nitrogen is withdrawn as overhead.

The oxygen-enriched liquid is reduced in pressure to approximately 1 atm and fed to a second lower pressure fractionation zone in heat exchange relationship with the first fractionation zone, where the oxygen-enriched liquid is partially evaporated and compared to A liquid bottom product of virtually pure oxygen is obtained.

Partial evaporation of the liquid in the second low pressure zone assists in decondensation of the liquid in the high pressure zone.

Nitrogen withdrawn from the top of the first high pressure zone is expanded through a turbine and passed in countercurrent heat exchange relationship with the fractionation zone;
This provides the necessary additional cooling for the partial condensation of the oxygen-rich liquid in the first fractionation zone.

The relatively pure oxygen liquid withdrawn from the bottom of the low pressure fractionation zone is evaporated either as a liquid or by condensation of a small portion of the air charge introduced into the first fractionation zone of the fractionator. , can be extracted from the system.

The waste nitrogen stream that ultimately leaves the heat exchange passage of the fractionator is passed through the reversing passage of the reversing heat exchanger.

The gaseous oxygen product stream is passed through a separate non-reversing passage of the reversing heat exchanger.

The fractionator process is such that there is only a temperature difference of approximately 1.7°C (3R) between both the exhaust nitrogen stream and the oxygen product stream and the charge air at the cold end of the inverting heat exchanger. will be implemented.

On the other hand, in the method of my patent No. 3,508,412, nitrogen enters the regenerative cooler at approximately 5.6°C (10R) below the dew point of the charge air.

Furthermore, as long as there is a sufficient quantity of exhaust nitrogen gas through the reversing passage of the heat exchanger to effect complete sublimation of the precipitated carbon dioxide and water vapor, both oxygen and some amount of gaseous nitrogen can be produced as pure products. The system can be changed to extract it.

The volume of the exhaust stream when both nitrogen and oxygen are removed as products must be greater than 50 times the total volume of the charge air stream.

That portion of the charge air that is removed at an intermediate point in the inverting regenerative heat exchanger is exited from the exchanger at an upstream point or on its cold end, thereby being transferred to the cold section of the heat exchanger. creating a mass imbalance.

This is the temperature pinch (△T) at the cold end of the heat exchanger.
, thereby ensuring complete sublimation of solid CO2 from the charge when the exhaust nitrogen and charge air passages are reversed to allow the exhaust flow to pass through the passage previously occupied by the charge stream. Assure.

On the contrary, when using a higher charge pressure of the order of 8 atmospheres, as for example in the case of the above-mentioned patent 3,508,412, the temperature difference between the charge air and the separated stream through the regenerative cooler is inversely The exchanger works (4.4℃ (8R)
Must be less than or equal to

If the temperature difference at the cold end of the reversing regenerator between the incoming air stream and the nitrogen product and oxygen rich exhaust stream is increased, operating at a charge pressure of 3 atmospheres using the above patented method. If the temperature is greater than 1.7° C. (3R), the exhaust stream will not sweep up and remove CO3 which could clog the regenerator.

These relationships are illustrated in Figure 1 of the drawings.

The method of separating oxygen from air according to the invention basically consists of the following.

Charge air containing water vapor and CO2 is compressed to a relatively low pressure, the compressed charge air stream is passed through a first passage of an inverting heat exchanger, and nitrogen is removed through a second passage of the heat exchanger. passing in heat exchange relationship with the air flow, thereby causing the water vapor and CO3 in the charge air to freeze on the surface of said first heat exchanger passage, reversing the two flows, thereby directing the nitrogen exhaust stream to said first heat exchanger passage. 1 passage, the charge air stream is passed through the second passage to cause sublimation or evaporation of the water vapor and the CO2, and at the end of this cycle, the compressed charge air stream is passed through the first passage. and then reversing the two flows again so that the nitrogen exhaust flow passes through the second passage, and repeating this cycle at predetermined intervals so that at an intermediate point in the heat exchanger one of the feed air streams is removed. The extracted portion of the charge air was further cooled by a heat exchanger in the separator, and the remainder of the cooled charge air was completely passed through it from the cold end of the heat exchanger. post-drawing, mixing said further cooled charge air portion with said withdrawn remaining cooled charge air stream, and passing said cooled charge air mixture through a first fractionation zone in said fractionator. , thereby condensing the oxygen-enriched liquid to produce a nitrogen overhead, withdrawing the oxygen-enriched liquid from the first fractionation zone, depressurizing the withdrawn oxygen-enriched liquid to a low pressure, and The depressurized liquid is passed downwardly into a second fractionation zone in the fractionator, thereby producing nitrogen vapor and producing an oxygen-enriched liquid product from the second fractionation zone as a product. withdrawing the oxygen-rich liquid, work-expanding the overhead nitrogen from the first fractionation zone and discharging the cooled nitrogen under reduced pressure, and transferring the cooled work-expanded nitrogen to the second fractionation zone. passing through a passageway in said fractionator in heat exchange relation with said zone and extracting heat from said zone, said nitrogen being withdrawn from said last-mentioned passageway in said fractionator, said withdrawn waste nitrogen stream being passing as described above through one of said first and second passages of said reversing heat exchanger into the cold end of said reversing heat exchanger; Heat exchange and fractionation in the above-mentioned fractionation device is carried out by a small fraction between the exhaust nitrogen stream entering the cold end of the heat exchanger and the cooled charge air stream withdrawing from the cold end of the heat exchanger. It should be carried out under conditions where there is no difference in temperature.

If at least a portion of the oxygen-enriched liquid product withdrawn from the second fractionation zone is recovered as gaseous oxygen, the charge air mixture collects such portion of the oxygen-enriched product before passing through the first fractionation zone. It is further cooled through heat exchange with
This causes evaporation of gaseous oxygen from such products.

Such gaseous oxygen may then be passed through the third passage of the inverting heat exchanger in heat exchange relationship with the charge air stream.

Referring to FIG. 2 of the drawings, the air is compressed to about 3 atmospheres at 10, cooled to near ambient temperature at 12, and the liberated water is separated in a separator at 14.

The air charge then passes through a reversing valve 16 and enters a reversing regenerative heat exchanger, generally designated 18.

This reversing valve 16 is connected to two passages 20 and 22 of a reversing regenerative heat exchanger 18 comprising three units A, B and C as well.

The heat exchanger includes a heat exchange passage 20 for the feed air, a heat exchange passage 22 for the exhaust nitrogen, and also a heat exchange passage 24 for the oxygen product.
Contains.

A reversing valve 16, together with a check valve assembly such as 26, which will be more fully described hereinafter, causes a charge air of 3 atmospheres in passage 20 to be alternated with a discharge of nitrogen at 1 atmosphere in passage 22. .

As the charge air in 20 is cooled in countercurrent heat exchange with the nitrogen exhaust stream in 22 and the oxygen product in 24, water vapor and CO
2 is frozen on the surface of the heat exchange passage 200.

After a predetermined period of time, e.g. 7 minutes and 30 seconds, the reversing valve 16 is actuated to redirect the charge air to the passageway 22 previously occupied by the nitrogen exhaust stream and to direct the low pressure nitrogen exhaust stream to the passageway 22 previously occupied by the air stream. The CO2 and water vapor freeze to sublimate and evaporate the gas.

In a typical factory, heat exchangers are designed so that a complete cycle occurs every 15 minutes.

A portion of the charged air, for example 4 volumes, is approximately -163'C (
198 R) at a tap point (outlet) 28 and passed through a check valve 26 to a gel trap 30, which may contain silica gel, charcoal, or molecular sieves, to remove every last trace of CO2; The air then passes through the high-pressure evaporation zone 44 and the low-pressure evaporation zone 52, which are in close heat exchange relationship with each other.
It is further cooled in the heat exchange passages 32 of a fractionator 33 having a temperature of 1.5 mm and exits at 34 at -175° C. (176 R) at approximately 3 atmospheres.

Passage 32 extends in heat exchange relationship with the bottom portion of low pressure evaporation zone 52 .

The remainder of the air charge is further transferred to passage 2 of unit C of heat exchanger 18.
It is further cooled at 0 and exits at 36 at about -175°C (176R).

34 is mixed with air charge 36 and the mixture is passed through line 38 to heat exchange passage 3 of oxygen product evaporator 40.
9, where a small portion of the charge is partially condensed by evaporating the oxygen product, as described further below.

42 air mixture is charged to the bottom of high pressure fractionation zone 44 operating at 3 atmospheres.

As a result of the non-adiabatic differential evaporation that takes place in this zone, the oxygen-rich liquid is converted into pure nitrogen at 46%
gradually condenses from the upwardly moving vapor until it is removed as the top of the column.

The oxygen-enriched liquid is withdrawn from the bottom of the high pressure separation zone at 48, reduced to 1 atmosphere by a liquid level control valve 50, and charged to the low pressure separation zone 52, which is operating at 1 atmosphere.

Nitrogen-rich vapor is gradually evaporated from the descending liquid until the oxygen-rich products up to oxygen 95 are removed as bottoms at 54 as a result of the non-adiabatic differential black zone in zone 52;
The product evaporator 40 is charged via line 56 .

Oxygen vapor at approximately -177°C (173R) exits 58 and enters passage 24 at the cold end 59 of heat exchanger 18 in countercurrent heat exchange relationship with the air charge in passage 20.

Warm oxygen product exits heat exchanger 18 at 61.

High pressure fractionation zone 44 in heat exchange relationship with low pressure fractionation zone 52
It is noted that is substantially shorter than band 52 and extends a distance midway through the height of band 52.

The overhead nitrogen exiting to 46 from high pressure fractionation zone 44 is warmed in heat exchange passage 60 to about -177°C (173R);
While still at 3 atm, the nitrogen discharge pressure was reduced to 1 atm and the temperature at 66
The temperature is lowered to approximately -194°C (142R).

If desired, the turbine 62 may be loaded by a compressor 64, which is used to increase the pressure of warm oxygen at 61 to the oxygen product at 65.

The cold nitrogen vapor at 66 is directed to a heat exchange passage 68 in the fractionator 33 where it passes through the fractionation zone 52 at low pressure or 1 atm.
First, cooling is applied to decompose the oxygen-rich liquid.

This liquid passes downwardly in zone 52 while the nitrogen, which contains only a small amount of oxygen, is removed as overhead at 70.

This nitrogen stream is mixed with nitrogen turbine exhaust 66 and the resulting exhaust nitrogen mixture stream is further warmed in heat exchanger passages 68 until it exits 72 at 1177°C (173R,).

This then enters the passageway 22 at the cold end 59 of the heat exchanger 18 which is only 1.7° C. (3R) cooler than the charge air 36 exiting the cold end 59 of the heat exchanger 18 .

If liquid oxygen is desired, it is removed via valve 14 in line 56 or 75.

There are additional difficulties with reversing exchangers when liquid oxygen is the desired product, as noted above.

Due to the mass imbalance in the return flow in the regenerator, △
The temperature difference between the T profile or return flow and the air charge in the heat exchanger upstream of the Tahoe expander tap at 28 is no longer constant and as the temperature of the air charge decreases △T increases.

This phenomenon limits the amount of liquid that can be withdrawn as product.

This difficulty is solved by adding a second intermediate tap at 80 in the heat exchanger at a warmer location than the first tap at 28.

A portion of the charged air is extracted at about -129 DEG C. (260 R), passes through a check valve 82 and a gel trap 84, and then passes through a turbine 85 where it is expanded to 1 atmosphere at about -163 DEG C. (198 DEG R).

The cool expanded air then passes through check valve assembly 86 and exits exhaust 22 at point 88 in the exchanger and at point 28 where the air is withdrawn through heat exchange passageway 32.
to go into.

If only oxygen-enriched liquid is desired, the mixture of chilled air streams 34 and 36 in the chilled air feed stream 38 is fed directly to the high pressure fractionation zone 44 and the oxygen at 54 from the low pressure fractionation zone 44 is fed directly to the high pressure fractionation zone 44. Any oxygen-enriched liquid is removed as an oxygen-enriched liquid product 55 and no oxygen-enriched product passes through passage 24 of regenerative exchanger 18.

According to the variant shown in FIG. 3, the tumbler paths, designated 90 and 91, provided in the units B and C of the reversing exchanger (trumbler passages: heat exchange channels 90 and 91 in FIG. 3, Used in a reversing heat exchanger instead of the gel trap 30.

All incoming air is cooled along its entire length in Figures 3A, B, and C, water vapor CO3 is completely removed, and some of the purified charge air is brought to the desired temperature for the 32 population in the first tumbler pass 91 ( For example 198 R) and the rest at a temperature suitable for the turbine 85 population (for example 282 R)
It is then heated in the second tumbler path 90.

) may be used in place of the 28 and 80 air bleeds.

The charge air is at the cold end of the heat exchanger at 92 - 175
Completely cooled to 176°C (176R).

The portion to be cooled in the heat exchanger passage 32 is then cooled to -163°C (198R) in the tram puller passage 91 of unit C.
warmed by.

The remaining portion of the air to be charged to the turbine 85 is further warmed to -116°C (282R) by passing through the second tram puller passage 90 of unit B.

Trampuller passages are useful in certain cases.

Because if you use this, 30 and 84 gel traps and 2
This is because some of the check valves 6 and 82 are removed.

Although this reduces equipment and maintenance costs, the disadvantage is that it cannot efficiently handle load changes.

Tramp puller passages should therefore only be used if a constant load is maintained.

If only oxygen gas is desired, there is no need to provide airflow at 80 or use the second tram puller passage 90, and there is no need to use the second turbine 85.

According to the variant shown in FIG. 4, means are provided to increase the total oxygen recovery of the fractionator by supplying liquid nitrogen reflux to the top of the low pressure fractionation zone 52.

Three atmospheres of nitrogen vapor is also vented in line 61 or alternatively directly from the high pressure fractionation zone 46 prior to expansion in the turbine.

A flow control valve 94 controls the amount of nitrogen removed and the remainder is expanded in turbine 62.

Nitrogen is transferred to line 4 by passage 950 through heat exchanger 98.
It is condensed in heat exchange relationship with the reduced pressure oxygen-rich liquid in 8, the pressure is reduced in valve 96, and the 10
0 to the top of the low pressure fractionation zone or alternatively 66
is mixed with the turbine exhaust gas at , thereby providing increased cooling to the upper portion of low pressure fractionation zone 52 .

The primary advantage of this variant is that it increases the total recovery of oxygen so that essentially all the oxygen in the charge air is recovered, reducing the total power consumption for the production of gaseous oxygen products. However, the disadvantage is that it increases cost and reduces the cooling available from turbine 62, thereby reducing the amount of oxygen that can be recovered as a liquid product.

Accordingly, the present invention includes several novel features.

One of these features is that the heat exchange in the reversing heat exchanger 18 and the mass transfer zone in the non-adiabatic differential distillation unit 33 regenerate the temperatures of both the exhaust nitrogen stream and the oxygen product stream leaving the Kurobe unit. The method is such that the temperature at the cold end of the heat exchanger is only slightly below the charge air temperature, i.e. 1.7°C (3R).

This allows for easy removal of solid carbon dioxide and water from the charge air passageway by exhaust flow during reversal of the charge air and exhaust flow.

Another novel feature is the use in the system of a fractionator having a high-pressure fractionation zone and a low-pressure fractionation zone, where the oxygen-enriched liquid withdrawn from the high-pressure fractionation zone is
The oxygen-rich product is then charged to a low-pressure fractionation zone.

A portion of the charge air passes in heat exchange relationship with the lower portion of the low pressure fractionation zone and the entire charge air mixture passes in heat exchange relationship with the oxygen-enriched liquid product before being charged to the high pressure fractionation zone.

The overhead nitrogen streams from both the high pressure and low pressure separation zones pass in heat exchange relationship with the charge air in such separation zones, although the overhead nitrogen stream from the high pressure separation zone is further cooled by expansion. to maintain a low temperature differential between the incoming nitrogen exhaust and oxygen product streams 22 and 24 and the outgoing air charge stream at the cold end 59 of the inverting heat exchanger.

Another novel feature is the implementation of the process so that a reversing heat exchanger can be used while producing liquid oxygen and gaseous oxygen products or only oxygen gas.

From the above, the present invention aims to reduce the amount of frozen C in the charging air passage.
A novel method and system for separating oxygen from air using a differential distillation apparatus in conjunction with an inverted regenerative heat exchanger under process conditions such that 02 and water are easily removed from the heat exchanger. You can see that it is by providing.

Although particular embodiments of the invention have been described for purposes of illustration, since various changes and modifications may be made within the spirit of the invention, the invention should not be construed as limited by anything other than the scope of the appended claims. It will be understood that this is not the case.

[Brief explanation of the drawing]

FIG. 1 shows the temperature difference along the length of an inverting heat exchanger between the feed air stream and the separated stream, including the nitrogen exhaust stream. FIG. 2 shows a schematic flow diagram of the preferred mode of operation. FIG. 2a is a modification of the system illustrated in FIG. 2 for the production of only an oxygen-enriched liquid as product. FIG. 3 is another variation illustrating an inverted heat exchanger that uses a tumbler pass instead of a gel trap. FIG. 4 is yet another modification of the system illustrated in FIG. 1 to increase total oxygen product recovery. 10: Air compressor, 12: Air cooler, 14: Water separator, 16: Reversing valve, 18: Reversing heat exchanger A, B, C52
0: Heat exchanger passage (for air), 22: Heat exchanger passage (for exhaust nitrogen), 24: Heat exchanger passage (for oxygen), 26
: Check valve, 28: Charge air tap point air bleed, 30 Niger trap, 32: Heat exchange passage, 33: Separator (having high pressure evaporation zone 44 and low pressure evaporation zone 52), 3
4: Air outlet, 36: Air outlet, 38: Pipeline,
39: Heat exchange passage of oxygen product evaporator, 40: Oxygen product evaporator, 42: Air mixture, 44: High pressure fractionation zone, 4
6: Pure oxygen overhead, 48: Oxygen-enriched liquid, 50: Control valve, 52: Low pressure fractionation zone, 54: Bottoms, 56: Pipeline, 58: Oxygen vapor outlet, 59: Heat exchanger Cooling end, 60: Heat exchange passage, 61: Oxygen product outlet, 62:
turbine, 63: turbine feed, 64: compressor, 65: oxygen product, 66: cold nitrogen steam turbine exhaust, 68: heat exchange passage, 70: nitrogen overhead, 72: exhaust nitrogen leaving the heat exchanger; 74: Valve, 75: Oxygen vent, 80:
Heat exchanger second intermediate tap air bleed, 82: Check valve, 84 Nigel trap, 85: Turbine, 86: Check valve, 88: Point where drain liquid 22 enters the exchanger, 90 Nidrum puller, 91 Nidrum puller, 92 : cold end of heat exchanger,
94: Flow control valve, 95: Heat exchanger passage, 96: Valve, 9
8: heat exchanger, 100: top of low pressure fractionation zone.

Claims (1)

[Scope of Claims] 1. Compressing the charge air containing water vapor and CO2 to a pressure of about 3 atmospheres or less, and compressing the air in a heat exchange relationship with the exhaust flow of nitrogen through the second passage of the reversing heat exchanger. passing the charged feed air stream through a first passage of a reversing heat exchanger, thereby causing the water vapor and 002 in the charge air to freeze on the surface of said first heat exchanger passage, and reversing the two flows. , thereby flowing a nitrogen exhaust stream through the first passage and flowing the charge air stream through the second passage to cause sublimation or evaporation of the water vapor and the CO2, and at the end of the cycle a compressed charge air stream. reversing the two flows again such that the nitrogen flow passes through said first passage and the nitrogen exhaust flows through said second passage, and repeating this cycle at predetermined intervals, At an intermediate point, a portion of the feed air stream is withdrawn and the withdrawn portion of the charge air is further cooled in heat exchange relationship with the lower part of the second fractionation zone in the fractionator, from the cold end of the heat exchanger. withdrawing the remainder of said cooled charge air stream after passing through it completely; mixing said further cooled charge air portion with said remaining cooled charge air flow; The charged air mixture is passed through a first fractionation zone in the fractionator, thereby condensing the oxygen-enriched liquid and creating a nitrogen overhead, and removing the oxygen-rich liquid from the first fractionation zone. extracting the extracted oxygen-enriched liquid to a low pressure, and directing the reduced pressure liquid downwardly into a second fractionation zone in heat exchange relationship with the first fractionation zone in the fractionation apparatus. passing the oxygen-enriched liquid through the first fractionation zone to produce nitrogen vapor and produce an oxygen-enriched liquid, withdrawing the oxygen-rich liquid as product from the second fractionation zone, and removing the overhead nitrogen from the first fractionation zone to work. discharging the expanded and vacuum-cooled work-expanded nitrogen, passing the cooled and work-expanded nitrogen through a passageway in the fractionator in countercurrent heat exchange relationship with the upper part of the second fractionation zone; removing heat from the separator, removing the nitrogen from the last-mentioned passageway in the fractionator, and inverting the removed nitrogen stream into the cold end of the heat exchanger. The heat exchange in the reversing heat exchanger and the fractionation in the fractionator are carried out in the manner described above through one of the first and second passages of the vessel at a pressure of about 3 atm. The gap between the exhaust nitrogen stream entering the cold end of the heat exchanger and the cooled charge air stream also withdrawn from the cold end of the heat exchanger at an operating pressure of
R) A method of separating oxygen from air, comprising carrying out the process under conditions of only a small temperature difference. 2 Compressing the charge air containing water vapor and CO2 to less than about 3 atmospheres, passing the compressed charge air stream through a first passage of an inverting heat exchanger and passing nitrogen through a second passage of said heat exchanger. passing in heat exchange relationship with the nitrogen exhaust stream, thereby causing the water vapor and CO2 in the charge air to freeze on the surface of the first heat exchanger passage, reversing the two flows, thereby causing the nitrogen exhaust stream to freeze on the surface of the first heat exchanger passage. flowing through the first passageway and flowing the charge air stream through the second passageway to cause sublimation or evaporation of the water vapor and the CO2; at the end of the cycle, the compressed charge air stream passes through the first passageway; passing through the passageway, reversing the two flows again such that the nitrogen exhaust flow passes through the second passageway, and repeating this cycle at predetermined intervals, replacing the cooled charge airflow with the A portion of the cooled charge air stream is withdrawn from the cold end of the vessel after passing completely through it and passed through a trampuller bath and returned through a reversing exchanger. withdrawing at least a portion of said portion at an intermediate point of said heat exchanger; further cooling said withdrawn portion of said charge air in a heat exchange relationship within said fractionating device; said remainder of said cooled charge air stream; from the cold end of the heat exchanger after passing completely through the heat exchanger, mixing the further cooled portion of the charge air with the withdrawn remainder of the cooled charge air stream; The cooled charge air mixture is passed through a first fractionation zone in the fractionator thereby condensing the oxygen-rich liquid and removing the nitrogen overhead from the first fractionation zone. withdrawing the liquid, reducing the withdrawn oxygen-enriched liquid to a low pressure, and directing the reduced pressure downwardly into a second fractionation zone in heat exchange relationship with the first fractionation zone in the fractionation apparatus. passing through a fractionation zone thereby producing nitrogen vapor and producing an oxygen-enriched liquid; and withdrawing said oxygen-enriched liquid as product from said second fractionation zone; and nitrogen overhead from said first fractionation zone. The nitrogen that has been cooled and expanded while doing work is discharged under reduced pressure, and the nitrogen that has been cooled and expanded while doing work is transferred to the second
Heat is extracted from said zone by passing it through passages in said fractionator in countercurrent heat exchange relationship with said fractionation zone, said nitrogen is withdrawn from said last-mentioned passage in said fractionator, said extracted waste is passing a nitrogen stream as described above into the cold end of the inverting heat exchanger through one of the first and second passages of the inverting heat exchanger; heat exchange and fractionation in the above-mentioned fractionation apparatus at an operating pressure of less than about 3 atmospheres with a waste nitrogen stream entering the cold end of the heat exchanger and withdrawn from the cold end of the heat exchanger. A method for separating oxygen from air comprising carrying out under conditions where there is only a small temperature difference of about 1.7° C. (3R) between the exiting cooled charge air stream. 3. Means for compressing the feed air containing water vapor and CO2 to below about 3 atmospheres; an inverted heat exchanger including first and second passages; Freezes on the surface and is sublimed and evaporated by reversing the flow of the feed air stream from the first passage to the second passage and the flow of the nitrogen exhaust stream from the second passage to the first passage. Valve means for alternately reversing the flow of feed air from a first passage to a second passage and vice versa from the second passage to the first passage in the heat exchanger, such as valve means operable to repeat the cycle at predetermined intervals; means for withdrawing a portion of the flow of charge air at an intermediate point in the exchanger; a check valve for passing said flow of charge air; a fractionation apparatus comprising a first fractionation column and a second fractionation column, the said withdrawn portion of the charge air being in heat exchange relationship with the lower part of the second fractionation column for further cooling the said withdrawn portion of the charge air; means for withdrawing the remainder of said cooled charge air stream from the cold end of said heat exchanger after its complete passage; said further cooled charge air portion and said cooled charge air; means for mixing the withdrawn remainder of the stream; means for passing the cooled charge air mixture through the first fractionation column, thereby condensing the oxygen-enriched liquid and discharging the nitrogen overhead; means for extracting the oxygen-rich liquid from the second fractionation column; means for reducing the pressure of the extracted oxygen-rich liquid to a low pressure; means for passing said second fractionating column in exchange relationship, thereby producing nitrogen vapor and producing an oxygen-enriched liquid; means for withdrawing said oxygen-enriched liquid as a product from said second fractionating column; an expander; a means for passing the nitrogen radicals and tops from the first fractionating column through the work expander and discharging the cold work-expanded nitrogen under reduced pressure; a passage means in the second fractionating column; means for passing the expanded nitrogen through the last-mentioned passage means in heat exchange relationship with the second fractionation column; removing nitrogen from the last-mentioned passage; and removing the nitrogen from the last-mentioned passage; Apparatus for separating oxygen from air, comprising means for passing as a nitrogen exhaust stream into the cooled end of the heat exchanger through one of the first and second passages of the inverting heat exchanger as described above.